Most vehicle indicator lights are equipped with a parabolic type reflector for forming a beam of rays running essentially parallel to an emission direction (or reference axis) of the light from a light source which is disposed close to the focus of the reflector.
However, in some cases such a reflector is omitted.
A first such case is when the lights are required to be very shallow ("flat" lights) because of lack of space for receiving deeper lights on the vehicle. The absence of such reflector results from the physical impossibility to include such a reflector in the small space allowed for the light since such reflectors are necessarily relatively deep.
Another case is when the reflector is omitted for reasons of economy, since the reflector is relatively expensive compared with the other parts of the light. In this case the fact that the light is shallow derives from the fact that the reflector has been omitted.
Finally, a shallow indicator light that does not have an internal reflector may be used for reasons of style.
Nevertheless it is still generally necessary, even without a reflector, to form a light beam which is relatively concentrated along the emission axis in order to satisfy the photometric requirements laid down by regulations.
A well-known solution to this problem consists in forming a beam of essentially parallel light rays by means of a Fresnel lens disposed in front of the lamp and incorporated either in its closure glass, or else separated therefrom. Such a Fresnel lens is conventionally constituted by a succession of nested rings each of which is in the form of a portion of spherical lens focused on the filament of the lamp which constitutes the light source in the light.
In the above-defined context, such Fresnel lenses are advantageous in that they enable an indicator light beam to be formed using a light whose depth is very small, for example a few centimeters.
Nevertheless, Fresnel lenses suffer from several drawbacks: they take a relatively long time to manufacture and are therefore relatively expensive, since the master pattern for making the mold used for forming the glass comprises a large number of different spherical surfaces each of which must be defined accurately. This accuracy requires that each ring should be relatively wide. As a result, the beam obtained has a clearly perceptible succession of light zones corresponding to the ring-shaped spherical refraction surfaces, and dark zones corresponding to the steps between these surfaces. This constitutes a second drawback. In addition to the unsightly appearance of the beam, there may be further difficulties in meeting the photometric requirements with any given beam.
The present Applicant's published French patent application No. 2 501 828 describes an indicator light of the above type in which the recovered light flux is increased by providing a reflector device behind the lamp and operating on the catadioptric principle to return the rays reflected by the lamp back through 180.degree. towards the lamp.
However, this device merely creates a virtual light source which is practically superposed on the real light source and as a result the above-mentioned optical defect remains.
The present invention seeks to mitigate these drawbacks of the prior art by proposing a shallow indicator light which is easy and cheap to make while nevertheless providing a light beam which is satisfactory from the points of view both of optics and of appearance.